Boys are no longer lagging behind girls when it comes to reading ability, according to a new report.

After examining the reading habits of over 210,000 primary and secondary school children from 1,237 schools across the UK, the What Kids are Reading 2012 report found that the gap between girls' and boys' reading abilities appears to be closing. "We can no longer claim that boys read at a lower level of difficulty than girls so overall under-achievement must be caused by other factors," wrote the report's author Professor Keith Topping of Dundee University.

Although in some academic years girls are continuing to outperform boys, on balance across years one to 11 the reading gender divide is closing, the report said. Using software to analyse the level of difficulty of books, researchers found that across all years, there were four cases when the difficulty level of books read by boys was greater than girls, three cases where girls' difficulty was greater than boys, and two cases where it was equal.

"In the first years, children are reading very difficult books with a high degree of success – it is wonderful what reading motivating books does for children," said Topping, a professor of educational and social research. From year nine, however, the average book difficulty level declines, which he called "alarming".

Roald Dahl remained the most popular writer for children, followed by young children's author Roderick Hunt. Jeff Kinney's bestselling Diary of a Wimpy Kid series – "notable for its relatively high readability", said the report – propelled him into third place, while Francesca Simon came in fourth, "proving the popularity of her Horrid Henry series amongst boys". JK Rowling was fifth, with Allan Ahlberg, Stephenie Meyer, Jacqueline Wilson, Michael Morpurgo and Dav Pilkey rounding out the top 10. "Allen Ahlberg has lost a good deal of popularity from last year, but still does relatively well, especially with girls," wrote Topping. "For girls, Stephenie Meyer is now more or less equal with Jacqueline Wilson. For boys, Dav Pilkey, Michael Morpurgo and Robert Muchamore feature. Girls tended to choose books with female role models."

Literacy consultant Bev Humphrey said the popularity of Muchamore and Wimpy Kid creator Kinney among schoolchildren was "pleasing to note as they write very 'boy orientated' books, and the fact they are so high on the report bucks the previously perceived 'boys don't read' trend".

Topping urged teachers to be aware of the "marked differences" in reading preferences between girls and boys, and stressed the importance of "sustaining a higher level of challenge in children's reading", particularly as they transfer to secondary school, where the difficulty of books being read drops away. "Boys are more interested in non-fiction but need encouragement to read it carefully," he concluded. "Boys are particularly likely to read books that are too easy, and their reading needs closer monitoring than that of girls. Even high-achieving readers do not challenge themselves enough as they grow older."

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